Weathercatch: The cause of our historic heatwave? Location, location, location

Unprecedented. Dangerous. Prolonged. Those are the terms used by the National Weather Service Spokane to describe this week’s most extreme heat wave of the Pacific and Inland Northwest region in recorded history.
And it’s not even the peak of summer yet.
Unless you’ve been blissfully locked away in an air conditioned room since last Saturday, you’ve felt the stifling heat. And if you’ve been following the news and weather reports, you know we’re in the throes of the hottest weather in the region’s history.
High temperatures rose well above 100 degrees this week – from Spokane, Yakima and Moses Lake to Seattle and Portland.
Even the overnight lows have been remarkably high. And not just for a day or two, but multiple days in a row.
On Sunday, some 2,100 athletes competing in the Coeur d’Alene’s Ironman triathlon battled temperatures reaching 101 degrees and pavement temperatures exceeding 120 degrees. Race organizers supplied 62,000 pounds of ice at hydration stations along the route, as well as misting stations.
Then, as the heat peaked in many Inland Northwest locations on Tuesday and Wednesday, temperatures ran as much as 40 degrees above normal. Cooling stations were set up in Washington and Idaho to help keep people safe.
What’s causing this historic heat wave?
Mostly, an atmospheric condition known as a heat dome, or a bubble-like zone of high pressure. These occur when high pressure in the upper atmosphere acts as a lid and prevents hot air from escaping. This, in turn, causes air to sink to the earth’s surface, turning warmer on the way. Heat domes are fairly common during summer , but not this particular one.
What’s unusual is its location. Instead of being centered over the desert Southwest and overlapping into the Pacific Northwest, this heat dome is situated smack-dab over our region, stretching north into British Columbia. In fact, last Sunday, the Canadian town of Lytton soared to 115 degrees, becoming the first place in Canada to record a temperature that high, according to the country’s weather agency. By the way, that’s just one degree less than the hottest temperature of 116 recorded in Las Vegas.
What’s also unusual about this heat dome is its intensity, how locked in it is atop the region, and that it arrived in June. Heat domes typically develop in late July or August. The fact that it’s occurring so early in summer makes it all the more extraordinary.
And talk about persistent. Likely the Pacific Northwest’s “most prolonged heat wave in recorded history,” according to the weather service, this heat dome is taking its time moving out. Triple-digit heat is expected to last until this Sunday, the Fourth of July, when the high temperature is expected to finally drop to – are you ready? – a “cool” 98 degrees in Spokane.
Contributing to the heat wave’s intensity and duration is an entrenched drought caused by a very dry spring. Hot, parched soil is emitting yet more heat into the ground surface and also the air.
The deepening drought and early heat wave may well be setting up the Pacific Northwest for a fiery summer. Of most immediate concern is the elevated risk of fires this Independence Day weekend. Please use extra caution. A single spark is all it will take.
Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek. Weiford can be reached at ldweiford@gmail.com.